Answer
$y=5cos(\frac{1}{4}x)$
Work Step by Step
1. The given graph resembles to $y=cos(x)$, with a general form $y=A\ cos(\omega x)$,
2. We can find the amplitude$A=5$, period$=8\pi$, phase shift$=0$.
3. We have $\frac{2\pi}{\omega}=8\pi$, thus $\omega=\frac{1}{4}$
4. Thus we have $y=5cos(\frac{1}{4}x)$
